1. Field of the Invention
The present invention relates to an armrest provided on the lateral wall of an automotive seat, and in particular relates to a locking mechanism for such an armrest, in which the arm rest is retained generally horizontally in a use position and upright in a non-use position.
2. Description of the Prior Art
In the past, an armrest of the type provided laterally of a seat has been equipped with various different kinds of locking mechanisms. However, most of the hitherto proposed locking mechanisms for that arm rest are rather complicated in structure and not so simple in its operation. For example, there have been known two typical armrest locking mechanisms respectively from the Japanese Laid-Open Publication No. 57-160415 and U.S. Pat. No. 3,807,799.
In the former Japanese prior art, the locking mechanism comprises a disc-like lock plate provided in a seat back and a disc-like stopper plate fixed on the armrest, the lock plate having a pair of projected pieces and the stopper plate having plural holes rowed circularly therein. By operating a lever, the lock plate is moved towards or withdrawn from the stopper plate, so that the projected pieces of the former are engaged into or disengaged from corresponding ones of the plural holes of the latter. Thus, the engagement and disengagement of the projected pieces into and from the holes of the stopper plate lead to the locking and unlocking of the armrest for its positional adjustment. However, the operating procedures of this prior art require the operation of the lever to unlock the armrest, then the manual rotation thereof at a desired use position, and again the operation of the lever to lock the armrest at that position, which causes an annoyance. Its structure is complicated, with a large number of components.
According to the latter U.S. prior art, the armrest locking mechanism disclosed therein comprises a bracket fixed on the seat back, a square hole perforated in the bracket, a rotational shaft of the armrest, and a square plate fixed on the rotational shaft. With this structure, the locking of the armrest is effected by fitting the square plate into the square hole in place in order to retain the armrest in a horizontal use position or an upright non-use position, and its unlocking is effected by disengaging the square plate from the hole, allowing rotation of the armrest. Yet, such locking and unlocking action is aided by the biasing force of spring, and especially the unlocking operation involves the step of moving the armrest outwardly from the seat back so as to disengage the square plate from the hole. Consequently, this prior art is not simplified in structure sufficiently and still leaves an annoying operation problem.
Thus, the conventional armrest locking mechanism has been defective in that it requires a great number of components and increased costs for assembling the same, and its operation efficiency remains to be improved.